There occasionally arises pains or tumors when a vein is partly clogged with a thrombus. One method of treatment for such troubles is by the removal of thrombi through a thrombus-removing device which is inserted percutaneously. This method, however, involves a possibility of causing pulmonary embolism in the case where the thrombus which has entirely or partly peeled off the vascular wall reaches the lung together with the blood flow. A common countermeasure to avoid this trouble is to use a thrombolytic agent before and after treatment and/or during treatment, or to remove by suction as many thrombi as possible during treatment. Such measures, however, still have the possibility that some peeled thrombi large enough to cause clinical problems reach the lung.
One of the known methods for avoiding pulmonary embolism involves the use of a filter to catch and collect thrombi flowing through the blood vessel, as shown in U.S. Pat. No. 8,562,637 for example. This filter takes on a net-like shape, so that it is inserted into the blood vessel while it is contracted and then it is expanded in the blood vessel.
The filter disclosed in U.S. Pat. No. 8,562,637 has difficulties in catching and collecting small thrombi because it expands in the blood vessel, which results in an enlarged mesh size. It also has a disadvantage of requiring a high power in the case where the thrombi caught and collected by the filter are sucked off against the strong blood flow.